The present invention relates to steering wheels for vehicles, and more particularly to steering wheels that are formed integrally with a pads and a ring cover.
A typical steering wheel has an annular gripping ring, a pad located at the center of the ring, and spokes extending from the ring toward the center of the steering wheel. The ring includes a metal ring core and a ring cover, which covers the ring core. The spokes include metal spoke cores and a spoke cover, which covers the spoke cores. The spoke cores are connected to a boss, which is located below the pad. The boss couples the steering wheel to a steering shaft. In general, the boss is mounted on the distal end of the steering shaft by a fastener such as a bolt.
An air bag device and other devices are mounted on the steering wheel after the spoke cores and the boss are secured to the steering shaft. The pad is then mounted over the air bag device.
Steering wheels having a cover and a pad that are formed integrally (see Japanese Unexamined Utility Model Publication No. 2-133955) have been proposed. The integrally formed pad and cover improves the appearance of the steering wheel.
Since the pad and the cover are formed integrally, the steering wheel has no opening above the boss. Therefore, the spoke cores and the boss are separately assembled to the steering shaft. Specifically, the boss is secured to the steering shaft. Then, spoke cores, to which an integrally formed pad and cover are attached, are secured to the boss.
However, coupling the spoke cores to the boss causes the following problems. The spoke cores are secured to the boss by two bolts, which are lateral with respect to the steering shaft, at right and left sides of the boss. When securing the spoke cores to the boss, a certain accuracy is required in the position of the spoke cores in relation to the boss. However, the spoke cores are sometimes secured to the boss without the required position accuracy. That is, the position of the cores sometimes deviates from the required position with respect to the boss. Further, the dimensional accuracy of the part of the spoke cores fastened to the boss differs between products. This may permit causes the spoke cores to move relative to the boss.
In a typical steering wheel, the pad is pressed for activating a horn. In a steering wheel having an air bag device, a horn switch mechanism is located between the air bag and the pad. Recently, a sheet-like horn switch such as membrane switch has been used, which provides enough room for an air bag in the steering wheel.
The membrane switch constitutes a part of a horn switch circuit and includes upper and lower thin metal plates facing each other. The upper plate is located directly below the pad and the lower plate is located directly above the air bag. Insulating spacers are located between the upper and lower plates for defining a space between the plates. Normally, the spacers separate the plates from each other. Projections are formed on a surface of the upper plate. A back board is located on the back of the lower plates. The back board improves the rigidity of the lower plate.
When the pad is pressed, the projections on the upper plate are also pressed. This deforms the upper plate and causes the upper plate to contact the lower plate. Accordingly, the horn switch circuit is closed and the horn is activated.
However, the prior art steering wheels have the following drawbacks.
(1) Thin metal plates in membrane switches are easily deformed by temperature changes. The deformation of the plates may cause the plates to contact each other thereby activating the horn even if the pad is not pressed. In other cases, deformation of the plates results in the pad having to be pressed harder in order to activate the horn.
(2) Since a membrane switch includes several parts (metal plates, spacers located between the metal plates, a back board), the assembly of the switch is burdensome. Further, the assembly of the switch requires high accuracy to prevent erroneous operations of the switch. This raises the manufacturing cost of the steering wheel.